Brian wrote a song also off of the third album, Days Before You Came Hear in this song we have subtle allusions to the use of various drugs, however the one that sticks out the most to me, is the reference to heroin use. This is the verse:

"Thunderbolts and lightning
Each day a brand new vein
Couldn't start to hide me
Each tourniquet colliding
Didn't want you anyway"

Now this reference could seem very incoherent to some, which, you later realize is all a part of Brian's Style, and I mean that in the most endearing of ways.

Allright the overall message of the song Days Before You Came is that the singer's life feels empty without this person. And so when this person comes to town, things start to brighten up.

Days before you came
Counting breaths inside me
Even crack cocaine
Couldn't start to hide me

Ok that part right there seems to say that when this person shows up, the singer wants to spend as much time with them as possible, so he starts doing coke to stay awake all the time. As time goes on his "baby" starts to look worn down and during his claims to revitalize him, we get the heroin reference. Thus indicating he's become addicted to this person:

In stating such a thing we see that this is where the addiction becomes unhealthy. Just like remaining co-dependent on a person you've just broken up with is looked on as being bad, wrong, or making you seem slightly Obsessive. And that my dear darlings is why Heroin makes an excellent metaphor for love and relationships. Though its vile, it's nearly impossible to put down forever, and when you do you're never the same person again!